A museum object has a different perspective, based mainly on relative humidity. The room relative humidity will clearly follow outside fluctuations closely if there is a steady ventilation with outside air. It is important to realize that as soon as we introduce room heating or cooling, we can no longer go by the outside relative humidity values without calculating changes due to temperature. It can be said that the key factor in museum climatology is relative humidity, too high, too low or too variable. The architect's main worry in the tropics is solar heat gain -- in the heating of the inside of the building by sun's rays. Solar heat gain can be reduced by (i) shading; (ii) reflection; (iii) ventilation; (iv) low thermal capacity. An important job of air conditioning is to control the relative humidity and temperature. Light causes so much damage that, wherever a museum is in the world, its lighting must be brought under control. Since textile and works of art on paper commonly fade more quickly at higher humidities, lighting control becomes even more important in the humid tropics. See also: <i>AATA 12-48. -- AATA